The objective of the invention is a method and a device for collecting oil mixed with ice blocks.
As a consequence of ships striking a rock, colliding or equipment failure, oil can get into the water. Collecting oil from water is especially difficult when the water is partly or fully covered by ice. The situation is particularly difficult when the oil is in a broken ice field, such as a fairway. In that case, oil is not only on the lower surface of the ice, but also mixed with the ice blocks and trash ice and, to some extent, even on top of the ice. Collecting oil from ice blocks by using the equipment on the market has not been efficient enough. The state of the art recognizes a low-gradient plane that pushes ice blocks under the surface of the water; as a result, part of the oil comes off, and the dispersed oil can be recovered by using various methods.
Patent publication FI 80746 describes an application on board a vessel to collect oil from among ice blocks. The application comprises a bow member with a low gradient, planar lower surface that is provided with intake openings for water containing impurities. When the vessel moves forward, ice blocks are submerged below the surface and are washed at the same time. According to the publication, intensive waterjets can enhance washing. The bow is a part that is separate from the actual body of the vessel and it can be lifted and lowered to achieve optimal driving conditions.
Patent application FI 73029 describes a method for collecting oil from a water level covered with ice. In the method, if needed, ice is broken into small enough pieces so that they can be submerged below the water level by using the equipment available. Oil, that comes off the ice blocks by washing with water streams that are generated by submerging the ice blocks, is recovered.
Patent application U.S. Pat. No. 4,039,454 describes a device for separating oil from water and floating ice blocks. This device also comprises an inclined plane that forces the ice blocks under water. The plane consists of a grating through which the oil can rise and be transferred to the collection equipment. Oil is removed from ice blocks when the ice blocks are submerged under the water.
Patent publication FI 75014 describes an application on board a vessel for collecting oil from among ice blocks. The lower surface of the vessel bow is low-gradient so that, when the vessel moves forward, ice blocks are submerged under the water, simultaneously being washed by the water. The lower surface of the inclined plane comprises bristles that sweep the upper surfaces of the ice blocks. The lower surface of the plane comprises water intake openings and the oil is separated from the water inside the vessel. The water that is pumped out is sprayed on the ice blocks from which the oil is to be removed.
In prior art solutions, the separation of oil from the ice blocks is solely based on the buoyant force of oil in relation to water, when ice blocks are forced under the water level. This separation method is not efficient and the majority of the oil remains attached to the ice blocks. By using the method and the equipment according to the invention, oil can be removed from ice blocks considerably more efficiently than before.
The objective of the invention is a method for separating oil from ice blocks, comprising forcing the ice blocks under the water along an inclined surface formed by a bar screen or a grating attached to the vessel. The method is characterized in that oil is separated from ice blocks by vibrating the inclined surface formed by the bar screen. Vibrating is preferably effected in an essentially vertical direction. The pounding movement of the bar screen now drives the ice downward and the buoyant force of the water returns them to the bar screen. As a result of the impacts, oil is detached from the ice and it rises to the water level above the bar screen, from where it can be collected by using various methods.
Another objective of the invention is a device for the method described above. The device, comprising an inclined surface formed by a bar screen or a grating for forcing ice blocks under water, is attached to the side or bow of the ship and, when the ship is propelled, a movement that forces the ice downwards is generated. The device is characterized in that oil is separated from the ice blocks by vibrating the inclined surface formed by the bar screen. Vibrating is preferably effected in essentially the vertical direction.